When Cat (Kristin Kreuk) and Vincent (Jay Ryan) make it their mission to capture Liam (guest star Jason Gedrick), they find information about a Patient X that they might be able to use to help them find him. Meanwhile, JT (Austin Basis) and Tess (Nina Lisandrello) work to confirm that JT is serum free. Nicole Gale Anderson also stars.

After the couple's botched wedding and Cat's reluctance to help in tracking beasts, this week fans will see her back in action with Vincent to stop Liam once and for all.

Vincent and Cat's highly anticipated wedding was halted as Juliana escaped prison and Liam attacked their wedding ceremony, killing Juliana in the process.

A new preview for Patient X shows a bloody crime scene, as Cat tells Vincent: "Liam doesn't care how many innocent people he kills."

We see JT Forbes in a police car with Tess, as Cat says: "We can only protect JT for so long," as JT tells someone on the phone,"Do you think it's a trap?"

Another scene shows Tess telling JT to run as Vincent comes running and a big explosion takes place.

The promo teases some intense fights ahead for Vincent, and it ends with Tess and Cat firing bullets at someone.

Previously E!Online reported, based on a "good source", that one of the prime characters would be in a life-and-death situation, and be admitted to hospital.